[ntp:questions] Re: Reference clocks - which?

Tapio Sokura oh2kku at iki.fi
Fri Oct 29 23:05:09 UTC 2004

Richard B. Gilbert wrote:
> A Motorola Oncore M12+T GPS receiver is available from Synergy Systems 
> <http://www.synergy-gps.com/>
> for around $200US.  This is far better than what you say you need.  It 

They also have used, but fully functional Oncore VPs for sale for 
something like 30-40 USD (see the excess inventory link on the front 
page). In addition to the GPS itself you need a suitable antenna and 
power supply along with 5 volt regulation and a max232 circuit for 
serial port level conversion.

Anyway, a GPS synchronized time server can be built for considerably 
under 100 USD, not counting the PC itself. You just need to tinker a bit 
with the additional circuits and provide some kind of housing for them 
and the GPS board. The timing performance of Oncore VPs is excellent, 
generally the performance of the whole system is more limited by the PC 
than the GPS receiver.

> requires that you be able site an antenna where it will have an 
> unobstructed view of the sky.

I run my 6 channel Oncore VP with a magmount antenna located indoors and 
it is working fine with an average of 1-2 satellites tracked. When the 
position hold feature of the GPS receiver is used, one satellite is 
enough for timing. Of course more is better and more reliable, but you 
can make do with a quite limited view of the sky as well.


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